Got a barn find Suzuki LT80. Has not run for 15 years. Put on new carburetor new piston and rings and skimmed jug gust to get some cross hatches. It starts right up and ideals for about 5 minutes and then locks up. The I turn the fan by hand to free up and it will start right up again and run fine for another 5 minutes. I did not take bottom end apart but washed it out with parts cleaner and it seemed to turn over fine. Could my problem be with the clutches?